Boron-oxygen Complex Research Articles

Transformations in phenylboronic acid at high pressures and temperatures

A recent report on obtaining the n-type conductivity in diamonds doped with boron–oxygen complexes in a metal solvent (X. Liu et al., PNAS 2019) stimulates interest in the synthesis of diamonds in heterohydrocarbon systems with oxygen and boron. The simultaneous effect of boron and oxygen heteroatoms on phase transitions in a hydrocarbon system is examined in phenylboronic acid C6H5B(OH)2 at pressures of 7–8.5 GPa and temperatures up to 1600 °C. At pressures of about 7 GPa and temperatures up to 1100 °C, the transformation of the precursor occurs through the stage of polymerization into a graphane-like phase with the subsequent formation of nanographite. Micro- and nanodiamonds are synthesized at 8.5 GPa and 1600 °C from the initial precursor and nanographite, which is a product of preliminary carbonization, respectively. Despite the presence of oxygen and boron in the growth system, the n-type conductivity in diamonds and nanographite is not detected. It is found that the degree of boron doping of diamond in hydrocarbon systems decreases in the presence of oxygen with a high chemical affinity to boron and that nanodiamonds in the carbonized product can be obtained when volatile components leave the system.

Borate configuration and surface pre-functionalization effects on the boronizing behavior and corrosion inhibition

Surface boronizing treatment, which forms lattice defects between the boronized layer and the metal substrate, is an effective anti-corrosion strategy. We explored the bonding mode between boron-oxygen ligands and Fe substrate. [BO3] is bonded to Fe with Fe-B bonds, while [BO4] tends to form Fe-O bonds. The larger coordination number of B and O is beneficial to resist Cl- attack. Furthermore, carbon steels were amino-functionalized through a silanol condensation reaction. The electronic localization shifted toward Fe, which was conducive to the formation of hydrogen bonds between amidogen and boron-oxygen complex anions, which increased the boronizing efficiency by tenfold.

First principles investigation on the boron-oxygen complexes in diamond

The co-doping mechanism of boron and oxygen substitutional complexes in diamond are investigated since the B-O co-doping seems to be a solution for preparing n-type diamond in some experiments. We use first-principles calculations to predict the geometry of a range of B-O complexes in diamond. Three possibly stable configurations are confirmed through the formation energy and binding energy. We also find that B-rich complexes are more stable when O sits in the centre position, whereas O tends to be closer to another O in the case of O-rich complexes. Electrically, the former shows a shallow acceptor property while the latter is a neutral impurity by analysing the transition levels, band structures and partial density of states. Our calculation suggests that the B-O scheme may not be a feasible way for effective n-type diamond, but it might be a good method to prepare high-quality p-type diamonds.

Suppression and compensation effect of oxygen on the behavior of heavily boron-doped diamond films

This work investigates the suppression and compensation effect of oxygen on the behaviors and characteristics of heavily boron-doped microwave plasma chemical vapor deposition (MPCVD) diamond films. The suppression effect of oxygen on boron incorporation is observed by an improvement in crystal quality when oxygen is added during the diamond doping process. A relatively low hole concentration is expected and verified by Hall effect measurements due to the compensation effect of oxygen as a deep donor in diamond. A low acceptor concentration, high compensation donor concentration and relatively larger acceptor ionization energy are then induced by the incorporation of oxygen; however, a heavily boron-doped diamond film with high crystal quality can also be expected. The formation of an oxygen–boron complex structure instead of oxygen substitution, as indicated by the results of x-ray photoelectron spectroscopy, is suggested to be more responsible for the observed enhanced compensation effect due to its predicted low formation energy. Meanwhile, density functional theory calculations show that the boron–oxygen complex structure is easily formed in diamond with a formation energy of –0.83 eV. This work provides a comprehensive understanding of oxygen compensation in heavily boron-doped diamond.

Synergistic influences of titanium, boron, and oxygen on large-size single-crystal diamond growth at high pressure and high temperature

The synergistic influences of boron, oxygen, and titanium on growing large single-crystal diamonds are studied using different concentrations of B2O3 in a solvent–carbon system under 5.5 GPa–5.7 GPa and 1300 °C–1500 °C. It is found that the boron atoms are difficult to enter into the crystal when boron and oxygen impurities are doped using B2O3 without the addition of Ti atoms. However, high boron content is achieved in the doped diamonds that were synthesized with the addition of Ti. Additionally, boron–oxygen complexes are found on the surface of the crystal, and oxygen-related impurities appear in the crystal interior when Ti atoms are added into the FeNi–C system. The results show that the introduction of Ti atoms into the synthesis cavity can effectively control the number of boron atoms and the number of oxygen atoms in the crystal. This has important scientific significance not only for understanding the synergistic influence of boron, oxygen, and titanium atoms on the growth of diamond in the earth, but also for preparing the high-concentration boron or oxygen containing semiconductor diamond technologies.

Tuning back side passivation for enhancing the performance of PERC solar cells

In the mono-crystalline silicon passivated emitter and rear cell (PERC), the back side passivation film made up of Al2O3 + SiNx:H stacks is the mainstream design. In this paper, the effect of the thickness of Al2O3 passivation layer on the performance of the solar cell was studied, and the correlation between the refractive index (RI) of SiNx:H layer and the efficiency gain of the solar cell after regeneration was analyzed. The results indicate that the thickness of Al2O3 layer needs to be balanced between the surface passivation and bulk passivation of SiNx:H, and the lower RI of SiNx:H layer shows a better hydrogen passivation capability. During the restoration of the solar cell efficiency, a thinner Al2O3 layer facilitates a faster stabilization of the boron-oxygen complexes. Finally, a new five-layer SiNx:H film was designed for the back side passivation film, and a conversion efficiency of 22.56 % was achieved, which is 0.05 % higher than that of the solar cell with a single-layer SiNx:H film.

Metastable acceptors in boron doped silicon: evidence of the defects contributing to carrier induced degradation

This work focuses on the recombination-enhanced reactions of boron related defects in compensated silicon and their impact on the electrical performance of silicon devices. Using deep level transient spectroscopy, we measured the defect spectra in the collector of 14 MeV fusion neutron irradiated p-n-p silicon transistors during forward current injection, as well as the corresponding degradation kinetics of both current gain and leakage current on the same device. Two hole traps at + 0.43 eV and + 0.53 eV are proved to be acceptors in the lower half of the gap with significant recombination enhanced effects. These metastabe acceptors degrade the current gain by changing the space charge distribution in the p-n-p structure and are linked with carrier-induced boron-oxygen complexes responsible for the minority-carrier lifetime degradation of silicon photovoltaics.

Boron–Oxygen Complex Responsible for Light‐Induced Degradation in Silicon Photovoltaic Cells: A New Insight into the Problem

Results available in the literature on minority carrier trapping and light‐induced degradation (LID) effects in silicon materials containing boron and oxygen atoms are briefly reviewed. Special attention is paid to the phenomena associated with “deep” electron traps (J. A. Hornbeck and J. R. Haynes, Phys. Rev. 1955, 97, 311) and the recently reported results that have linked LID with the transformation of a defect consisting of a substitutional boron atom and an oxygen dimer (BsO2) from a configuration with a deep donor state into a recombination active configuration associated with a shallow acceptor state (M. Vaqueiro‐Contreras et al., J. Appl. Phys. 2019, 125, 185704). It is shown that the BsO2 complex is a defect with negative‐U properties, and it is responsible for minority carrier trapping and persistent photoconductivity in nondegraded Si:B+O samples and solar cells. It is argued that the “deep” electron traps observed by Hornbeck and Haynes are the precursors of the “slow” forming shallow acceptor defects, which are responsible for the dominant LID in boron‐doped Czochralski silicon (Cz‐Si) crystals. Both the deep and shallow defects are BsO2 complexes, transformations between charge states and atomic configurations of which account for the observed electron trapping and LID phenomena.

Boron–oxygen complex yields n-type surface layer in semiconducting diamond

Diamond is a wide-bandgap semiconductor possessing exceptional physical and chemical properties with the potential to miniaturize high-power electronics. Whereas boron-doped diamond (BDD) is a well-known p-type semiconductor, fabrication of practical diamond-based electronic devices awaits development of an effective n-type dopant with satisfactory electrical properties. Here we report the synthesis of n-type diamond, containing boron (B) and oxygen (O) complex defects. We obtain high carrier concentration (∼0.778 × 1021 cm-3) several orders of magnitude greater than previously obtained with sulfur or phosphorous, accompanied by high electrical conductivity. In high-pressure high-temperature (HPHT) boron-doped diamond single crystal we formed a boron-rich layer ∼1-1.5 μm thick in the {111} surface containing up to 1.4 atomic % B. We show that under certain HPHT conditions the boron dopants combine with oxygen defects to form B-O complexes that can be tuned by controlling the experimental parameters for diamond crystallization, thus giving rise to n-type conduction. First-principles calculations indicate that B3O and B4O complexes with low formation energies exhibit shallow donor levels, elucidating the mechanism of the n-type semiconducting behavior.

Evolution of the light sensitive defects in high performance multicrystalline silicon wafers

Sequential degradation measurements have been performed on passivated high performance multicrystalline silicon wafers, first at room temperature under low intensity illumination followed by a higher intensity illumination at an elevated temperature. The presence of two main degradation mechanisms, affecting the lifetime under different conditions has been demonstrated, namely, the well-studied light induced degradation caused by boron-oxygen-complexes and the less understood light and elevated temperature induced degradation. Light and elevated temperature induced degradation is the main lifetime limiting the recombination path when fully activated, but the contribution from boron-oxygen complexes is not negligible. This separation of the two degradation mechanisms might, therefore, be necessary for proper evaluation of the dominant recombination mechanism. Experiments also show regeneration of the minority carrier lifetimes caused by deactivation of both the lifetime limiting defects at comparable time scales, and under similar illumination and temperature conditions. Wafers from different heights in a high performance multicrystalline silicon ingot have been evaluated to better understand the underlying causes for the different degradation mechanisms. Effects of the iron-boron-splitting on the carrier lifetime are only visible in ungettered wafers.

Photovoltaics literature survey (no. 149)

Photovoltaics literature survey (no. 149)

КОМБІНАЦІЙНЕ РОЗСІЮВАННЯ СВІТЛА У СКЛОПОДІБНОМУ Li2B4O7

Lithium tetraborate is a promising material to be used in the production of solid electrolytes and solid-state batteries. A powerful tool for investigating its structure in the B2O3–Li2O system is Raman spectroscopy. The Raman spectra were investigated using the XploRA PLUS (HORIBA Jobin Yvon) Raman spectrometer at the temperature of T = 300 K within the 70–2000 cm–1 range. The excitation wavelength was 785 nm, the spectral resolution was no worse than 1 cm–1. As a result of the study, we have determined the nature of vibrational modes. We detected a fine structure in the 70–400 cm–1 range, which we found to correspond to normal vibration of the lithium-oxygen structural complexes in the structure of [LiO6] frames, and also vibrations and librations of [LiO6] frame and the BO3 and BO4 groups in the structure of [B4O7]2– cluster as a whole. In the 400–800 cm–1 range the superposition of vibrations of [LiO4] clusters and [BO4] tetrahedrons takes place, whereas their normal vibrations are detected in the 800–1354 cm–1 range. In the 1300–2000 cm–1 range we observed the manifestation of two-phonon states, the normal vibrations of borate rings, and the symmetric stretching of the BO3 flat triangles, and detected two peaks that have not been observed previously. The obtained results show that the Raman spectra of glassy Li2B4O7 generally display a single-mode behavior and are caused by a combination of vibrations of different types which are interconnected via the frame structure of the glass consisting of complex boron-oxygen and lithium-oxygen structural complexes.

Kinetic suppression of boron–oxygen complexes in p-type Czochralski silicon by tin doping

The impact of tin (Sn) doping on boron–oxygen (B–O) complexes responsible for light-induced-degradation (LID) in p-type Czochralski silicon has been investigated. It is found that Sn can effectively suppress the formation of B–O complexes, with increased activation energies and pre-exponential factors during both generation and dissociation processes, which are essentially attributed to the associated compressive strain as well as the formation of energetically favorable SnB complex, as revealed in experiment and by first-principle calculation. The results demonstrate the influence of Sn doping on the LID and strongly suggest its promising applications in photovoltaic industry.

Kinetics of the permanent deactivation of the boron-oxygen complex in crystalline silicon as a function of illumination intensity

Based on contactless carrier lifetime measurements performed on p-type boron-doped Czochralski-grown silicon (Cz-Si) wafers, we examine the rate constant Rde of the permanent deactivation process of the boron-oxygen-related defect center as a function of the illumination intensity I at 170°C. While at low illumination intensities, a linear increase of Rde on I is measured, at high illumination intensities, Rde seems to saturate. We are able to explain the saturation by assuming that Rde increases proportionally with the excess carrier concentration Δn and take the fact into account that at sufficiently high illumination intensities, the carrier lifetime decreases with increasing Δn and hence the slope of Δn(I) decreases, leading to an apparent saturation. Importantly, on low-lifetime Cz-Si samples no saturation of the deactivation rate constant is observed for the same illumination intensities, proving that the deactivation is stimulated by the presence of excess electrons and not directly by the photons.

Raman spectroscopy of crystalline, glassy, and molten states of lead diborate

Polarized Raman spectra of single crystals of lead diborate, PbB4O7 (PBO), are studied in detail at 300 K. The TO-, LO-, and IO-phonon lines of the A1, A2, B1, and B2 symmetries in the Raman spectra of this compound are assigned. Changes in the Raman spectra of the internal vibrations of boron–oxygen complexes upon transition from the crystalline to the glassy and the molten states of PBO are observed. On the basis of the obtained results, the regularities in the formation of boron–oxygen complexes in glasses, melts, and crystals of the PbO · 2B2O3, SrO · 2B2O3, and Li2O · 2B2O3. diborate compositions are analyzed.

Simulation Study of Light-induced, Current-induced Degradation and Recovery on PERC Solar Cells

The way to permanently recover the well-known Light-Induced Degradation (LID) which affects the p-type Cz-Si PERC solar cells represents one of the main challenges of photovoltaic research. In this work we have set up a numerical simulations flow which allows us to reproduce the experimental measured values of figures of merit (FOMs) of four different Cz-PERC solar cells lots subjected to a degradation and two regeneration processes. The recombination centres in bulk and the Boron-Oxygen complexes (B-O) are modeled by means of two trap levels tuned on the basis of experimental data. From simulations we confirm that the FOM degradation levels off after 16hours and the regeneration process characterized by relatively long time process is preferred in terms of performance recovery. In addition, further cells with different passivation films are analyzed by adopting the same methodology.

Injection-dependent Carrier Lifetime Analysis of Recombination Due to Boron-Oxygen Complexes in Wafers Passivated with Different Dielectrics by QSSPL and QSSPC

This paper compares the use of quasi-steady state photoluminescence (QSSPL) and photoconductance (QSSPC) measurements for injection-dependent carrier lifetime analysis of the state of boron-oxygen (B-O) complexes in boron-doped Czochralski wafers passivated with different dielectrics. Use of QSSPL measurements enabled effective carrier lifetime measurements over a larger range of injection levels than possible with QSSPC, potentially increasing the accuracy of estimates of the capture cross-section ratio of the deep-level B-O Shockley-Read Hall (SRH) defect. Although the capture cross-section ratios estimated using QSSPL (9.7 ± 1.7) and QSSPC (9.7 ± 1.9) for wafers symmetrically-passivated with silicon nitride and subsequently rapidly fired were very similar and close to the value of 9.3 reported by Rein et al. for the B-O defect, significant differences in the ratio and larger variances in the measurements within a group resulted for wafers with silicon nitride that was not annealed and wafers which were passivated with the thermal oxide. It is suggested the low-injection QSSPL measurements may introduce inaccuracies arising from the conduction of excited carriers via the diffused emitter away from the measurement area. This may suggest that there is little advantage in using QSSPL over the more commonly-used QSSPC measurements for these SRH analyses. Additionally, the study confirmed that stable regeneration of the effective carrier lifetime was only achieved when wafers were passivated with silicon nitride and underwent a rapid thermal anneal after deposition. If wafers were not rapidly thermally-annealed after silicon nitride deposition, then the recovery of effective lifetime observed with regeneration was not stable during a second light soak. Furthermore, the effective carrier lifetime of wafers passivated with a thermal oxide continued to decrease with light soaking, regeneration and a second light soaking with the appearance of “rings” in the PL images of oxide-passivated wafers as they underwent light soaking and regeneration highlighting the possible role of oxide precipitates in reactions occurring with light soaking and regeneration.

Impact of carbon co-doping on the performance of crystalline silicon solar cells

We have investigated the impact of carbon co-doping on the performance of boron–doped Czochralski-grown silicon solar cells. It is found that carbon co-doping will deteriorate the initial performance of Aluminium-back-surface-field solar cells before light-induced degradation (LID), owing to the enhancement effect on the formation of oxygen precipitation. However, carbon co-doping can effectively suppress the formation of boron-oxygen complexes in the solar cells, which becomes more significant with an increase of the carbon concentration. Therefore, the performance of carbon co-doped silicon solar cells is better than that of conventional silicon solar cells after LID. All these results are of great significance for the practical application of carbon co-doped silicon solar cells with low LID effect in photovoltaic industry.

Influence of the formation- and passivation rate of boron-oxygen defects for mitigating carrier-induced degradation in silicon within a hydrogen-based model

A three-state model is used to explore the influence of defect formation- and passivation rates of carrier-induced degradation related to boron-oxygen complexes in boron-doped p-type silicon solar cells within a hydrogen-based model. The model highlights that the inability to effectively mitigate carrier-induced degradation at elevated temperatures in previous studies is due to the limited availability of defects for hydrogen passivation, rather than being limited by the defect passivation rate. An acceleration of the defect formation rate is also observed to increase both the effectiveness and speed of carrier-induced degradation mitigation, whereas increases in the passivation rate do not lead to a substantial acceleration of the hydrogen passivation process. For high-throughput mitigation of such carrier-induced degradation on finished solar cell devices, two key factors were found to be required, high-injection conditions (such as by using high intensity illumination) to enable an acceleration of defect formation whilst simultaneously enabling a rapid passivation of the formed defects, and a high temperature to accelerate both defect formation and defect passivation whilst still ensuring an effective mitigation of carrier-induced degradation.

Ab-initio calculation study on the formation mechanism of boron-oxygen complexes in c-Si

Boron-oxygen (B-O) complex in crystalline silicon (c-Si) solar cells is responsible for the light-induced efficiency degradation of solar cell. However, the formation mechanism of B-O complex is not clear yet. By Ab-initio calculation, it is found that the stagger-type oxygen dimer (O2ist) should be the component of B-O complex, whose movement occurs through its structure reconfiguration at low temperature, instead of its long-distance diffusion. The O2ist can form two stable “latent centers” with the Bs, which are recombination-inactive. The latent centers can be evolved into the metastable recombination centers via their structure transformation in the presence of excess carriers. These results can well explain the formation behaviors of B-O complexes in c-Si.